1. Field of the Invention
The present invention relates to a manufacturing method of a ceramic matrix composite which is small in residual amounts of C and Si particles and high in airtightness.
2. Description of Related Art
To enhance performance of a rocket engine in which propellants such as NTO/N2H4 and NTO/MMH are used, it has been desired to raise a heat-resistant temperature of a combustor (thrust chamber). Therefore, a niobium alloy with a coating having a heat-resistant temperature of about 1500xc2x0 C. has heretofore been used as a chamber material for many rocket engines. However, this material is highly dense and heavy, a high-temperature strength of the material is low, and the coating has a short life.
On the other hand, ceramic has a high heat-resistance, but is disadvantageously brittle. Therefore, a ceramic matrix composite (hereinafter refered as CMC) reinforced with a ceramic fiber has been developed. That is, the ceramic matrix composite (CMC) is constituted of ceramic fiber and ceramic matrix. Additionally, the CMC is generally indicated as ceramic fiber/ceramic matrix by materials thereof. For example, when both materials are SiC, SiC/SiC is indicated.
Since the CMC is lightweight and has a high-temperature strength, the CMC is a remarkably promising material not only for the aforementioned rocket engine combustor (thrust chamber), but also for a high-temperature section fuel piping, jet engine turbine blade, combustor, afterburner component, and the like.
However, the conventional CMC has a problem that airtightness cannot be held, and thermal shock resistance is low. That is, for the conventional CMC, after a predetermined shape is constituted by a ceramic fiber, a matrix is formed in a fiber gap in a so-called chemical vapor infiltration method (CVI method). However, the CVI method has a problem that it takes an impracticably long period (e.g., one year or more) to completely fill the gaps among the fibers.
Moreover, to enhance the airtightness itself of the CMC, a polymer impregnate and pyrolysis method (PIP method) of simply impregnating a component of the ceramic fiber with molten material polymer and calcining the component is effective. However, since it is necessary to repeat an impregnating/calcining cycle many times (e.g., 40 or more times), the method is inefficient.
On the other hand, as an alternative CMC manufacturing method to the aforementioned CVI and PIP methods, a reaction sintering method (RS method) has locally been proposed (e.g., Japanese Patent Application Laid-Open No. 81275/1996 titled xe2x80x9cManufacturing Method of SiC Matrix Fiber Compositexe2x80x9d).
This method includes: forming the ceramic fiber into a three-dimensional structure having a predetermined shape; impregnating the three-dimensional structure with a starting raw material which contains silicon and carbon sources and forming a molded material having the predetermined shape; heating the resulting molded material in vacuum or inactive gas atmosphere at a temperature less than a silicon melting point, simultaneously pressurizing the molded material and reacting/sintering silicon and carbon to form an SiC matrix; and densifying the matrix.
FIG. 1 is a manufacturing process flow diagram of an SiC matrix long fiber composite by a reaction sintering method disclosed in xe2x80x9cDevelopment of Reaction-Sintered Silicon Carbide Matrix Long Fiber Compositexe2x80x9d (the 123rd committee presentation of results of a research on a heat-resistant metal material, Vol. 40, No. 3).
As shown in FIG. 1, in the RS method, an SiC fiber 1 coated with BN/SiC is braided on a monofilament surface, and a fiber preform 2 (three-dimensional structure) is formed. On the other hand, an SiC powder, C powder, dispersant, and water are compounded/mixed to form a matrix casting slurry 3. Subsequently, the fiber preform 2 is pressure-impregnated and cast with the matrix slurry 3. Finally, a green composite is heated at 1723 K in a vacuum furnace, impregnated with molten Si and reacted/sintered to complete a CMC.
However, the aforementioned RS method has a problem, in principle, that unreacted C and Si particles remain. That is, in the RS method, the fiber preform 2 is pressure-impregnated with the slurry 3 containing the SiC and C powder, subsequently the preform is heated at a temperature (e.g., 1723 K) which is not less than a silicon melting point (Si melting point is about 1683 K), and Si melting impregnation and reaction sintering are performed. However, during Si melting impregnation, excess Si remains. Another problem is that strength is considerably deteriorated during operation at the Si melting point or higher temperatures. Moreover, when an amount of Si is reduced during Si melting impregnation in order to avoid the problem, conversely C particles remain. This results in a problem that the strength is deteriorated by oxidation.
The present invention has been developed to solve the aforementioned problem. That is, an object of the present invention is to provide a manufacturing method of a ceramic matrix compound, in which only small amounts of C and Si particles remain, a matrix forming speed is high, and CMC having a high airtightness can be manufactured in a short time.
According to the present invention, there is provided a manufacturing method of a ceramic matrix composite, including steps of: mixing/dispersing a carbon powder (4) and a silicon powder (5) in solid phases; impregnating a woven fiber (2) with the powders; and subsequently exposing the woven fiber to a high temperature sufficient for reaction calcining to react/calcine the woven fiber.
Moreover, according to the present invention, a method includes: a mixing/dispersing step (13) of mixing/dispersing a carbon powder (4) and a silicon powder (5) in solid phases; a slurrying step (14) of adding a solvent and dispersant to a mixed/dispersed powder mixture to manufacture a slurry (8); an impregnating step (16) of impregnating a woven fiber (2) formed of an SiC fiber (1) with the slurry; and a reaction calcining step (18) of exposing the woven fiber resulting from the impregnating step to a high temperature sufficient for reaction calcining, and reacting/calcining the woven fiber to form a matrix portion.
According to the method of the present invention, the Si and C particles are uniformly dispersed/mixed beforehand with a ball mill, and the like, and the woven fiber is impregnated with the uniformly dispersed powder mixture and subsequently reacted/calcined so that an SiC matrix having no unreacted particle can be formed. That is, since SiC generation/reaction occurs in a uniformly dispersed state of the mixed/ground fine Si and C particles, no unreacted particle remains and reaction is easily controlled. Therefore, since this method is less troublesome than the conventional method, a manufacturing period can be shortened and cost can be reduced. Moreover, since the reaction calcining is performed in the vicinity of a silicon melting point at a sufficiently lowered temperature rise rate, a CMC having a high airtightness can be manufactured without leaving outflow of molten Si, or unreacted Si, C elements in the matrix.
According to a preferred embodiment of the present invention, the method includes a vacuum defoaming step (15) of reducing a pressure of the slurry (8) and removing a mixed gas after the slurrying step (14). By this vacuum defoaming step the mixed gas contained in the slurry is removed beforehand, and in the impregnating step (16) a filling ratio of particle mixture of Si and C particles can be enhanced.
Moreover, the method includes a tentative calcining step (17) of drying the woven fiber impregnated with the slurry and tentatively calcining the woven fiber at a temperature lower than the silicon melting point after the impregnating step (16). By this tentative calcining step the solvent and dispersant in the slurry are removed beforehand, and the reaction in the reaction calcining step (18) can efficiently be performed.
Other objects and advantageous features of the present invention will be apparent upon reading the following description with reference to the accompanying drawings.